Electrical to pressure (E to P) transducers are used in many fields for converting an electrical signal input to a pressure output for operating a pneumatic or hydraulic device. For example, the air flow in the heating and cooling system of an aircraft is often controlled by a pneumatically operated valve having an E to P transducer which comprises the pilot section of the valve. A frequently used assembly includes an electromagnetic device, such as a torque motor, for receiving an electrical signal input and for operating a flapper positioned near a nozzle in a variable orifice arrangement. The movement of the flapper is proportional in magnitude and direction to the input signal. The nozzle and flapper assembly is placed in series with a fixed orifice and is provided with a pressurized air supply. The stage pressure can be varied by varying the electrical supply to the torque motor and hence the position of the flapper.
A torque motor controlled flapper and nozzle arrangement functions well in controlled environments; however, in applications such as the aforementioned heating and cooling system of an aircraft this type of device often is unreliable in that it experiences extreme variations in environmental conditions which adversely affect its operation. For example, the stage pressure will vary with variations in the inlet pressure, and, in aircraft, changes in the engine operating conditions will affect the pressurized air supply and therefore the inlet pressure.
Yet another problem encountered, particularly with aircraft utilizing the aforedescribed variable orifice device, is that flow and pressure change with changes in the absolute pressure at the inlet and outlet. Thus, the controlled stage pressure will vary with altitude in that the absolute pressure decreases with increasing altitude. Since the stage pressure is extremely sensitive to flow, if changes occur in the fixed orifice, such as the accumulation of dirt particles which restrict the orifice, or if additional flow is drawn from the stage pressure cavity to operate the main valve or as the result of a leak occurring in the stage pressure cavities, the correlation between the variable orifice and the stage pressure will also change. The orifices and nozzles are highly sensitive to the accumulation of even minute particles of contamination, and integral filters are required to remove harmful contamination. However, the filters have not always functioned as effectively as desired.
Another problem encountered in pressure operated systems which experience extreme variations in environmental conditions is that pressure regulators often contain a compression spring or pilot pressure above a diaphragm for providing a bias force. To operate properly, the regulator must have a low spring rate or bias force, and conventional regulators are therefore sensitive to vibration. Because of the physical forces encountered in aircraft, vibration sensitive regulators do not function accurately.